The methods illustrated in FIGS. 15 and 16 are known as conventional methods of producing a semiconductor (silicon) wafer.
In the method of FIG. 15, firstly in a slicing step S110 a single-crystal ingot is sliced into wafers W; in a beveling step S120 the edge (circumference) of the wafer W is beveled; in a lapping step S130 the both surfaces of a number of wafers W are concurrently lapped with abrasive grain (free abrasive grain) being relatively coarse (i.e. batch lapping), which is followed by an etching step S140 and a mirror-surface polishing step S150. Thereby, the wafers W after subjected to the lapping are formed into final products.
The lapping step S130 will now be detailed. The lapping step S130 is carried out through the use of a lapping device 100 as illustrated in FIG. 17. The lapping device 100 includes a lower surface-plate 101 having an upward supporting surface 101a; an upper surface-plate 102 having a supporting surface 102a that overlies the supporting surface 101a of the lower surface-plate 101; a sun gear 103 disposed at the inner radius of the lower surface-plate 101; an internal gear 104 disposed at the outer circumference of the lower surface-plate 101; a carrier plate 105 that is interposed between the supporting surface 101a of the lower surface-plate 101 and the supporting surface 102a of the upper surface-plate 102 and that engages with the sun gear 103 and the internal gear 104; and a slurry supplying device 106 that supplies wafers W set inside respective holes 105a of the carrier plate 105 with a slurry containing relatively rough abrasive grain (free abrasive grain having a granularity of #1000 through #1500).
While the lower surface-plate 101 and the upper surface-plate 102 are rotating relatively to each other, the sun gear 103 and the internal gear 104 cause the carrier plate 105 to make planet motion, so that free abrasive grain supplied to the supporting surfaces 101a and 102a from the slurry supplying device 106 laps the both surfaces of a number of wafers W set in each hole 105a at the same time.
In the meantime, in a method shown in FIG. 16, in a slicing step S210 a single-crystal ingot is sliced into wafers W. In the subsequent grinding step S220 the top surface and the bottom surface of a wafer W one surface for each time is ground with abrasive grain (fixed abrasive grain) having a relatively coarse granularity (single-wafer grinding). The ground wafer W is then subjected to a beveling step S230, an etching step S240, and a mirror-surface polishing step S250 to be formed into a final product.
The grinding step S220 will now be detailed. In the grinding step S220 a grinding device 200 shown in FIGS. 18(a) and 18(b) is used. The grinding device 200 includes a turntable 201; a chuck 202 that overlies the turntable 201 and that vacuum sucks a wafer W; a grindstone support 204 that overlies the chuck 202 and having a grindstone 203 fixed thereto; and a grinding-water supplying device 205 that supplies a wafer W with grinding water. The grindstone 203 is formed of abrasive grain having a granularity of, for example, #300 through #1000.
While the turntable 201 and the grindstone support 204 are rotating relatively to each other and the grinding-water supplying device 205 is supplying the grinding water, the grindstone 203 is pressed against the surface of a wafer W, so that the top and the bottom surfaces of the wafer W is ground one surface for each time.
The lapping device 100 and the grinding device 200 are disclosed in Patent Reference 1.
However, processing wafers W in the methods of FIGS. 15 and 16 may sometime leave scratches on the surface of the mirror-polished wafer W. In other words, since in the lapping step S130 and the grinding step S220 carried out before the mirror-surface polishing relatively coarse abrasive grain is used, the subsequent normal mirror-surface polishing sometime does not completely remove all scratches on the surface.
For the above, as shown in FIGS. 19 and 20, finish grinding steps S135 and S225 are carried out after the lapping step S130 and the grinding step S220, respectively and before the mirror-surface polishing step S150 or S250, respectively. The finish grinding steps S135 and S225 use abrasive grain having a granularity of #2000 through #8000, such as resin-bonded grindstone, and which relatively encourages self-sharpening to finish the top and the bottom surface of a wafer W by polishing one surface for each time.